With
the number of TQWT/DTQWT kits sold, the quest for a
center speaker is becoming more frequent as surround fans want a
speaker to complement their (mostly) DTQWT systems.
This center speaker has been on the to-do list for a long time and
started as a "classic" horizontal d'Appolito set-up.
However, unless we cross over at a very low frequency between midbass
drivers and tweeter, we may experience crossover lobing, that is
uneven frequency response as we move from seat to seat in our home
cinema. Usually we have an even horizontal dispersion from
vertical aligned drivers if the chosen points of crossover have been
done with respect to the diameters of the drivers and slopes of
crossover. When wavelength
hits a value equal to the diameter of the driver, we start having
beaming (wellknown from fullrange drivers) and if the point of
crossover is above this frequency we may have irregularities off-axis.
Most good center speakers are - at least - 3-way. Some manufacturers
go even further and use a whole range of tweeters to overcome the
problem - like McIntosh.
Having the small SEAS MCA12RC 4" unit covering the 800-3000 Hz
range ensures wide dispersion and mated with the TW034 dome (this time
without waveguide) we are certain of overcoming this problem and
voiced around 92-93 dB, the MCA12RC can fill the gap between bass and
tweeter despite modest sensitivity compared to the other drivers. In
the end it even had to be attenuated 1 dB.

Due to smooth frequency response of all drivers,
an almost as simple as can be crossover.
I had hopes for 22 uF to middriver (cost) but 30 uF is what it takes.
Pay notice to L2021, DCR = 1.55 Ohm, no resistor needed here.

All interior panels damped with 10 mm felt material
except for panels behind 8008 drivers. Here we need space for mounting
crossovers; bass crossover
to one side, mid and treble crossover to the other side. On top of
crossovers a piece of folded 30 mm acoustilux is placed, 22 x 35 cm.
Pics to below.

Left: Horizontal dispersion @ 0, 5, 10, 15
and 20 deg. displaying an even power response over a wide area.
Right: Vertical dispersion starting at middriver height (red) and 5, 10, 15
and 20 deg. (black) above.
All in all this speaker has an even sound distribution over a wide area,
which was a prime target of the project.

Crossover layout for Option 1 (Superior-Z
version).
Same layout can be used for Option #2, all-STANDARD-Z-cap version,
although components take up considerably less space.
If you want to spoil your drivers, use WAX coils for L2041 and L1031
(both must be 16 AWG).

Layout for all-STANDARD Z-CAP version.
Click image to view large.
Due to small size caps, it can all be on one board.